JP7119369B2 - Distance measuring device - Google Patents

Description

The present invention relates to a distance measuring device having an oscillator that oscillates ultrasonic waves.

Patent Document 1 discloses an ultrasonic distance measuring device using a so-called Time-Of-Flight (TOF) method, which transmits ultrasonic waves, receives the reflected waves, and measures the distance to a reflecting object. is described.

This patent document 1 describes a distance measurement method for an ultrasonic distance measuring device that transmits an ultrasonic burst wave to which an identification signal (modulation signal) is added by modulating the frequency, phase, etc. of a pulse signal. .
According to this distance measurement method, a reflected wave of an ultrasonic wave or the like containing an identification signal as information is received and correlated with the transmitted modulation signal, so that the rising portion of the received reflected wave (received signal) can be detected with high accuracy. It is possible to detect and determine the distance.

Patent Document 2 discloses a vehicle surroundings monitoring device that detects obstacles existing around the vehicle by attaching a distance measuring device (ultrasonic sonar) to a vehicle and receiving reflected waves of transmission waves transmitted from the ultrasonic sonar. is described. Further, in such a vehicle surroundings monitoring device, there is a need for improving the detection performance of obstacles existing around the vehicle.

JP-A-2005-249770 JP 2011-112416 A

As described in Patent Document 1, adding an identification signal to an ultrasonic wave improves the detection accuracy of the rising portion of the received reflected wave. However, as exemplified in Patent Literature 2, in consideration of, for example, vehicle-mounted applications, it is not sufficient in terms of distinguishability between self-oscillated ultrasonic waves and ultrasonic waves from other distance measuring devices. Because many vehicles are running on the road, the ultrasonic waves generated by many vehicles are congested, and the identification signal included in the own ultrasonic wave and other vehicles are oscillating. This is because interference may occur in which the signals included in the ultrasonic waves overlap.
Therefore, it is desired to provide a distance measuring device that prevents interference between an identification signal contained in its own ultrasonic wave and a signal contained in ultrasonic waves oscillated by other vehicles.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a distance measuring apparatus that reduces the influence of interference and improves the measurement performance of distance measurement.

The characteristic configuration of the distance measuring device according to the present invention for achieving the above object is as follows:
an oscillator that oscillates a carrier wave;
a modulator that outputs a modulated wave obtained by adding an identification signal to the carrier wave in a predetermined manner;
an oscillation element that oscillates an ultrasonic wave corresponding to the modulated wave;
a receiving element that receives ultrasonic waves;
a demodulator that demodulates the ultrasonic wave received by the receiving element;
A control unit that determines the method of demodulated ultrasonic waves,
The control unit stores a frequency of the carrier wave oscillated by the oscillator and a modulation method of the modulated wave output from the modulator as a protocol setting of the ultrasonic wave to be oscillated by the oscillation element. has a part
When the modulator outputs the modulated wave, the control unit determines whether or not it is the first oscillation based on the setting of the protocol stored in the storage unit,
In the case of the first oscillation, the ultrasonic wave is received by the receiving element in advance, and the received ultrasonic wave is demodulated by the demodulator to obtain a demodulated signal. What is the protocol of the received ultrasonic wave? setting a different protocol and storing it in the storage unit, and outputting information about the setting of the protocol to the modulator;
If it is not the first oscillation, after reading the current protocol setting from the storage unit, the receiving element is made to receive an ultrasonic wave in advance, and the received ultrasonic wave is demodulated by the demodulation unit to generate a demodulated signal. and setting a protocol different from the protocol of the received ultrasonic wave based on the comparison result between the protocol of the received ultrasonic wave and the current protocol, and information about the setting of the protocol to the modulator output and
The modulator applies the identification signal to the carrier wave in a protocol different from the protocol of the received ultrasonic wave based on the information regarding the setting of the protocol, and outputs the modulated wave.

According to the above configuration, when an ultrasonic wave to which an identification signal is assigned is oscillated, the surrounding ultrasonic wave is received by the receiving element in advance, and the demodulated signal is obtained from the demodulator. It is possible to know the method of modulating the ultrasonic waves and the method of the demodulated signals of the surrounding ultrasonic waves such as the signals contained in the surrounding ultrasonic waves, that is, the method of modulating the surrounding ultrasonic waves. In the present application, receiving vibration means receiving vibration such as ultrasonic waves.
Therefore, the control unit outputs to the modulator information about the demodulation signal method, for example, information about the modulation method of the surrounding ultrasonic waves and the signal included in the surrounding ultrasonic waves, and the modulator is operated. Therefore, it is possible to assign the identification signal to the carrier wave by a method different from that of the demodulated signal.

As a result, the oscillating element can oscillate ultrasonic waves by applying an identification signal in a manner different from surrounding ultrasonic waves. After that, the control unit demodulates the ultrasonic waves received via the receiving element by the different method, distinguishes them from the signals contained in the surrounding ultrasonic waves, and uses the reflected waves of the ultrasonic waves oscillated by the self-oscillating element. It is possible to accurately determine whether there is an ultrasonic wave or another ultrasonic wave.
Therefore, according to the above configuration, it is possible to provide a distance measuring device that reduces the influence of interference with surrounding ultrasonic waves, particularly ultrasonic waves containing signals, prevents erroneous detection, and improves the measurement performance of distance measurement. can be done.

A further characteristic configuration of the distance measuring device according to the present invention is
The modulator outputs the modulated wave to which the identification signal having a bit arrangement different from that of the demodulated signal is added.

According to the above configuration, the control unit determines whether it is a reflected wave of an ultrasonic wave oscillated by its own oscillating element or another ultrasonic wave. A discrepancy allows for a more accurate determination. As a result, it is possible to correctly receive its own identification signal.

A further characteristic configuration of the distance measuring device according to the present invention is
The bit array has a bit length different from that of the demodulated signal.

According to the above configuration, the control unit determines whether it is a reflected wave of an ultrasonic wave oscillated by its own oscillating element or another ultrasonic wave. A discrepancy allows for a more accurate determination. As a result, it is possible to correctly receive its own identification signal. As a result, it is possible to correctly receive its own identification signal.

A further characteristic configuration of the distance measuring device according to the present invention is
The modulator outputs a modulated wave modulated by a method different from the modulation method demodulated by the demodulator.

According to the above configuration, the control unit determines whether it is a reflected wave of an ultrasonic wave oscillated by its own oscillating element or another ultrasonic wave. Discrepancies can be determined accurately.

A further characteristic configuration of the distance measuring device according to the present invention is
A piezoelectric element unit is provided as the oscillation element,
The vibration receiving element is a separate unit from the piezoelectric element unit.

According to the above configuration, the piezoelectric element unit used as the oscillation element only needs to be able to oscillate ultrasonic waves. For example, a unit having a piezoelectric element with a simple configuration can be obtained without requiring a circuit or control necessary for receiving ultrasonic waves. can. On the other hand, the receiving element only needs to be able to receive ultrasonic waves. For example, it can be a unit with a simple configuration optimized for receiving vibrations without requiring a circuit or control necessary for oscillating ultrasonic waves. It should be noted that units other than piezoelectric elements can be adopted as the unit that constitutes the vibration receiving element, so that the degree of freedom in the configuration of the distance measuring device increases, and a simple configuration can be adopted. Thus, according to the above configuration, the distance measuring device can have a simple device configuration.

Explanatory diagram of the configuration of the distance measuring device Diagram showing an example of vibration waveform Explanatory diagram of waveform modulated by phase modulation method Explanatory diagram of waveform modulated by amplitude modulation method Explanatory diagram of waveform modulated by frequency modulation method Explanatory diagram of detector configuration Explanatory diagram of distance measurement by TOF method Diagram explaining how to avoid false positives Explanatory diagram of vibration waveform modulated by multiple modulation methods Flowchart explaining the procedure for determining the modulation protocol Explanatory drawing of another configuration of the distance measuring device

A distance measuring device 100 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 11. FIG.

[Overview]
FIG. 1 is a schematic diagram for explaining a schematic configuration of the distance measuring device 100. As shown in FIG.
The distance measuring device 100 is a distance measuring device that measures the distance to the object 9 by receiving reflected waves of modulated ultrasonic waves.
This distance measuring device 100 is used, for example, as an in-vehicle obstacle detecting device (not shown), recognizes the presence of an object 9 as an obstacle, grasps the distance to the object 9, A case in which such information is notified to the driver will be described as an example.

A distance measuring device 100 includes a control unit 1 that controls the operation of the entire device and calculates a distance, a probe that has a piezoelectric element 3 that oscillates ultrasonic waves (an example of a receiving element and an oscillator element), and a piezoelectric element 3. and an oscillator 4 that oscillates the fundamental wave of the ultrasonic wave that oscillates.
Furthermore, the distance measuring device 100 mainly includes a modulator 2 that modulates the fundamental wave (carrier wave) oscillated by the oscillator 4, and a detector 5 that demodulates the reflected wave received by the piezoelectric element 3 to obtain a demodulated signal. provided as a functional unit.

[Description of details]
[Configuration of distance measuring device]
The following description mainly refers to FIG. 1, and refers to other figures as necessary.
The piezoelectric element 3 is a device that oscillates and receives ultrasonic waves.
The piezoelectric element 3 includes a vibrator (not shown) that is displaced in response to an applied voltage, and that generates an electromotive force in response to the displacement when a mechanical force such as vibration energy is applied. It is a probe consisting of a so-called ultrasonic transducer unit.
Since the vibrator of the piezoelectric element 3 resonates at a predetermined frequency (wavelength), normally, the center frequency (or wavelength) of the oscillating ultrasonic wave and the center frequency (or wavelength) of the receivable ultrasonic wave ) will be the same.
The resonance frequency of the piezoelectric element 3 of this embodiment is 40 kHz.

In this embodiment, the piezoelectric element 3 oscillates ultrasonic waves in response to changes in voltage applied from the modulator 2 . In addition, the piezoelectric element 3 can receive external vibration, for example, ultrasonic waves oscillated by the piezoelectric element 3 itself.

The piezoelectric element 3 used in this embodiment has constant energy that changes under predetermined (constant) conditions from the modulator 2 (in this embodiment, it changes at a frequency corresponding to the natural frequency of the piezoelectric element 3, When a constant amplitude voltage) is continuously applied, as shown in FIG. 2, after a plurality of vibrations, that is, after a predetermined delay time Td, a steady state is reached in which the constant amplitude A is reached.
Therefore, when it is desired to obtain a large amplitude with the piezoelectric element 3, a large delay time Td is required. On the other hand, when it is desired to obtain a relatively small amplitude with the piezoelectric element 3, the delay time Td is reduced.

In this embodiment, the piezoelectric element 3 repeats continuous vibration (vibration to which a voltage is applied) and stop for a predetermined time. When the piezoelectric element 3 stops vibrating, it can receive external vibrations (ultrasonic waves). In other words, voltage application is stopped when external vibration is received.
The vibration received by the piezoelectric element 3 is converted into a voltage signal by the piezoelectric element 3 and transmitted to the wave detector 5 .

That is, in the present embodiment, one ultrasonic transducer unit is used as the piezoelectric element 3, and the piezoelectric element 3 is used as an oscillation element when oscillating an ultrasonic wave corresponding to the modulated wave, and receives surrounding ultrasonic waves. When doing so, the same piezoelectric element 3 is used as a vibration receiving element.

The oscillator 4 is a frequency generator that oscillates a fundamental wave for vibrating the piezoelectric element 3 . A fundamental wave oscillated by the oscillator 4 is used as a carrier wave in this embodiment.
In this embodiment, the oscillator 4 generates a predetermined frequency based on the fundamental oscillation of a crystal oscillator (not shown) that vibrates at a predetermined frequency, and supplies it to the modulator 2 as a carrier wave.

The control unit 1 is a functional unit that controls the entire distance measuring device 100, and has a CPU 10, which is a central processing unit, as a core mechanism. The control unit 1 further includes a pulse generator 15 and a comparator 17 as main functional units, and further has a storage unit 19 in which an operation program for the control unit 1 is stored.

The pulse generator 15 is a signal generator that generates a signal containing a predetermined code. The pulse generator 15 generates a signal including a predetermined code unique to the distance measuring device 100 (a unique code string or a code string serving as an identification ID) as the identification signal.
The pulse generator 15 supplies (transmits) the generated signal to the modulator 2 in this embodiment.
The pulse generator 15 operates to generate a signal containing a predetermined code according to an operation command sent from the CPU 10 .

The pulse generator 15 generates a signal containing a binary code having a predetermined bit length and a predetermined bit arrangement.
For example, a bit length of 8 bits can be selected as the predetermined bit length.
Any arrangement may be selected as the predetermined bit arrangement.

The pulse generator 15 outputs each bit of a predetermined bit length as a pulse signal (pulse on/off). When the pulse generator 15 emits a pulse at a predetermined timing (pulse on), the pulse at the predetermined timing means binary 1, and when the pulse generator 15 does not emit a pulse at the predetermined timing (pulse off), the predetermined timing means zero.
If the bit length is 8 bits, the pulse generator 15 outputs a signal that is a combination of on and off pulses eight times.

Hereinafter, the state in which the pulse generator 15 generates a pulse at a predetermined timing is denoted by 1. A state in which the pulse generator 15 does not generate a pulse at a predetermined timing is defined as zero.
Further, when simply referred to as a pulse, it means either code 1 or code 0.
A pulse signal means a combination of a plurality of pulses.

The predetermined timing at which the pulse generator 15 emits the pulse can be synchronized with the timing (for example, period) of the fundamental wave oscillated by the oscillator 4, for example.
In this embodiment, it is synchronized with the cycle of the fundamental wave oscillated by the oscillator 4. Specifically, in principle, one pulse is emitted at each timing of eight wave oscillation (eight cycles). there is

The comparator 17 is an arithmetic unit for comparing the code contained in the signal (demodulated signal) obtained from the detector 5 and the code of the pulse generator 15 to determine whether they match or not.
The comparator 17 transmits the determination result (hereinafter referred to as determination result) to the CPU 10 .

The CPU 10 is a functional section that executes functions other than the pulse generator 15 and the comparator 17 in the control section 1 and is an arithmetic unit that operates according to a program stored in the storage section 19 .

The CPU 10 calculates the distance to the object 9 based on the determination result obtained from the comparator 17 and the timing of obtaining the determination result.
Further, the CPU 10, as the controller 1, instructs the modulation protocol to the modulator 2 under a predetermined condition.

In the present embodiment, the modulation protocol includes ultrasonic frequency, modulation method, setting of burst length of burst wave corresponding to each pulse generated by pulse generator 15, code information generated by pulse generator 15, and the like. means the method of As the control unit 1, the CPU 10 can instruct the modulator 2 about modulation protocols such as modulation scheme, burst length setting, and code information.

The modulator 2 is a modulation circuit (not shown) that modulates (hereinafter sometimes simply referred to as modulation) the fundamental wave oscillated by the oscillator 4 and transmits the modulated wave to the piezoelectric element 3. 3 has a circuit (not shown) to generate a voltage for driving .

In this embodiment, the modulator 2 uses the fundamental wave oscillated by the oscillator 4 as a carrier wave, modulates the fundamental wave according to the signal oscillated by the pulse generator 15, and generates a modulated wave containing signal information. . The modulator 2 applies the modulated wave to the piezoelectric element 3 as a voltage wave, that is, a voltage having a varying phase and amplitude to drive the piezoelectric element 3 . The piezoelectric element 3 vibrates according to the voltage applied from the modulator 2 and oscillates modulated ultrasonic waves, that is, ultrasonic waves containing signal information.

The modulator 2 can output a modulated wave to which an identification signal, which is a unique predetermined code, is assigned in a predetermined manner.
Here, the predetermined method means a modulation protocol.

In this embodiment, the modulator 2 can switch or combine a plurality of modulation protocols according to instructions from the control unit 1 for modulation.
The modulator 2 can switch and modulate a plurality of modulation schemes by switching a plurality of modulation protocols.
The modulator 2 can switch between at least a phase modulation method, an amplitude modulation method, and a frequency modulation method as a plurality of modulation methods.
In addition, the modulator 2 can use (combine or superimpose) a plurality of modulation schemes for modulation.

In this embodiment, the modulator 2 can simultaneously use at least two modulation methods out of the phase modulation method, amplitude modulation method, and frequency modulation method, and is compatible with each method. The modulator 2 includes a modulation circuit (not shown) for

In addition, the phase modulation method referred to in the present embodiment refers to a method in which a digital signal is expressed by changing the phase of a carrier wave and modulated, that is, a method of phase-modulating and transmitting, which is also called PSK (phase-shift keying). be called.

FIG. 3 shows an example of waveforms modulated by the phase modulation method.
In this embodiment, as shown in FIG. 3, the same phase as the carrier wave represents binary 1, and the phase shifted by π from the carrier wave represents binary zero.

Further, the amplitude modulation method referred to in the present embodiment refers to a method in which a digital signal is modulated by expressing a difference in the amplitude of a carrier wave, that is, a method of performing amplitude modulation, and is also called ASK (amplitude shift keying).
In this embodiment, a relatively large amplitude represents a binary one and a relatively small amplitude represents a binary zero of successive waves.

FIG. 4 shows an example of waveforms modulated by the amplitude modulation method.
In FIG. 4, with respect to a relatively large amplitude representing binary 1, when the amplitude is 100%, the amplitude of 50% is modulated as a target amplitude representing binary 0, and 100 It illustrates the case where amplitudes below 75 percent, which is the average of percent and 50 percent, are taken to represent a binary zero.

Further, the frequency modulation method referred to in the present embodiment refers to a method of expressing and modulating a digital signal by different frequencies of carrier waves, that is, a method of performing frequency modulation, and is also called FSK (frequency shift keying).

FIG. 5 shows an example of waveforms modulated by the frequency modulation method.
In this embodiment, the same frequency as the carrier can represent a binary 1, and a frequency shift from the carrier by a predetermined amount can represent a binary 0. For example, in the case of FIG. 5, the same frequency as the carrier wave represents a binary 1, and a frequency less than the carrier wave by a predetermined amount represents a binary zero.

The modulator 2 can switch between a plurality of modulation protocols, corresponding to each pulse generated by the pulse generator 15, and switch the burst length of the burst wave for modulation.
That is, in this embodiment, when zero is represented by the amplitude modulation method, a relatively small amplitude is obtained by shortening the burst length.

The detector 5 shown in FIGS. 1 and 6 is a functional unit having a demodulation function for demodulating the vibration received by the piezoelectric element 3 and obtaining a demodulated signal. In this embodiment, the vibration received by the piezoelectric element 3 is an ultrasonic wave, particularly a reflected wave of the ultrasonic wave oscillated by the piezoelectric element 3 .

In this embodiment, as shown in FIG. 6, the detector 5 includes an ASK demodulator 51 and an FSK demodulator as demodulator circuits that function as demodulators corresponding to at least the phase modulation method, the amplitude modulation method, and the frequency modulation method, respectively. It has a demodulator 52 and a PSK demodulator 53 .

The detector 5 also has a so-called FFT circuit 50 for analyzing the frequency of the ultrasonic wave received by the piezoelectric element 3 . The frequency information analyzed by the FFT circuit 50 is transmitted to the ASK demodulator 51, the FSK demodulator 52, and the PSK demodulator 53, respectively. FFT means Fast Fourier Transform.

The ASK demodulator 51 and the PSK demodulator 53 have independent frequency oscillators 51a and 53a, respectively. ing.

ASK demodulator 51 , FSK demodulator 52 , and PSK demodulator 53 transmit demodulated signals to comparator 17 as detector 5 . Upon receiving the demodulated signal, the control unit 1 determines the format of the demodulated signal and recognizes the signal included in the demodulated signal.

[Description of operation]
[Basic description of obstacle detection operation]
The detection of the obstacle 91 and the distance measurement operation by the distance measuring device 100 will be described below.
In this embodiment, the distance measurement device 100 measures distance by a so-called time-of-flight (TOF) method.
FIG. 7 shows a graph for explaining the basic concept of distance measurement by the TOF method.

The horizontal axis of the graph in FIG. 7 indicates the passage of time.
The vertical axis of the graph in FIG. 7 means the magnitude of amplitude.
A line E is an envelope of the amplitude of vibration of the piezoelectric element 3 .
In this embodiment, the piezoelectric element 3 oscillates modulated ultrasonic waves as described above. A specific example of oscillation of this modulated ultrasonic wave will be described later.

The piezoelectric element 3 is driven by the modulator 2 for an oscillation time T1 at predetermined intervals.
In FIG. 7, after the piezoelectric element 3 is driven by the modulator 2 to vibrate (forced vibration) for an oscillation time T1, it continues to vibrate due to inertia for a reverberation time T2 (so-called reverberation), and then vibrates from the outside. is received.

In the case shown in FIG. 7, the piezoelectric element 3 receives a vibration peak P1 exceeding a predetermined threshold value Th after a time Tp since the driving of the piezoelectric element 3 was started. This vibration peak P1 is usually the peak of the wave reflected from the obstacle 91 (see FIG. 1).
Note that the threshold Th is a value for distinguishing small reflected waves from the road 90 (for example, reflected waves due to unevenness of the road) from reflected waves from the obstacle 91 .
In this embodiment, a reflected wave having a peak exceeding the threshold Th is defined as a reflected wave from the obstacle 91 . On the other hand, a reflected wave having a peak that does not exceed the threshold Th is generally defined as a reflected wave caused by unevenness of the road 90 .

When measuring the distance to the obstacle 91 by the TOF method, the start point of the vibration peak P1 should be recognized as the start point of reception of the reflected wave.
The starting point of the vibration peak P1 is shown in FIG. 7 as a point that is a time ΔT before the time Tp. Usually, the length of time ΔT is equal to oscillation time T1. In other words, the time Tf required for receiving the reflected ultrasonic waves oscillated by the piezoelectric element 3 can be obtained by subtracting the oscillation time T1 from the time Tp.

For example, in the case of FIG. 7, the time from the time point (zero) when the driving of the piezoelectric element 3 is started to the time point preceding the time point Tp indicating the vibration peak P1 by time ΔT corresponds to the time point Tf. . Alternatively, the time from reaching the oscillation time T1 to reaching the time Tp indicating the vibration peak P1 is the same length of time as the time Tf.

A reflected wave received by the piezoelectric element 3 is demodulated by the detector 5 , and the extracted demodulated signal is sent to the comparator 17 of the control section 1 .
Here, the reflected wave of the ultrasonic wave oscillated by the piezoelectric element 3 has information including a predetermined code. Therefore, the signal demodulated and extracted by the detector 5 contains the predetermined code generated by the pulse generator 15 . Therefore, if the determination result of the comparator 17 matches, the control unit 1 recognizes that the reflected wave is the reflected wave of the ultrasonic wave oscillated by the piezoelectric element 3, and detects the existence of the obstacle 91. can be done. Then, the control unit 1 obtains the time Tf, and can recognize the distance to the obstacle 91 from the time Tf and the speed of sound.

[About avoiding false positives]
A supplementary explanation will be given regarding the case where the determination result of the comparator 17 is a mismatch.
In FIG. 8, in addition to the line E shown in FIG. 7, an incident ultrasonic wave having a vibration peak P2 is superimposed as a line Ef. This line Ef is obtained by receiving, by the piezoelectric element 3, an ultrasonic wave or a reflected wave thereof emitted by another distance measuring device mounted on another vehicle 200 (see FIG. 1), for example.

In the case shown in FIG. 8, the ultrasonic wave having the vibration peak P2 does not contain a signal containing a predetermined code. Therefore, even when the vibration peak P2 exceeds the threshold value Th, the comparator 17 determines that there is no match. It can be recognized that it is not a reflected ultrasonic wave.
In this way, by oscillating and receiving ultrasonic waves containing a predetermined code, the control unit 1 can avoid erroneous detection and improve the measurement performance of the distance measuring device 100. can.

[Regarding ultrasonic modulation]
The modulator 2 modulates according to a predetermined modulation protocol according to an instruction from the control unit 1 .
In this embodiment, the modulator 2 arbitrarily switches the modulation method in accordance with an instruction from the control unit 1, and oscillates a modulated wave by combining them.
Further, the modulator 2 modulates based on the information of the signal supplied from the pulse generator 15 as the controller 1 as described above. , the code information is changed as necessary. Therefore, the modulator 2 modulates with a predetermined bit length and a predetermined bit arrangement in response to a change in the information of the signal of the pulse generator 15 as an instruction from the control unit 1 .

Further, in this embodiment, the piezoelectric element 3 oscillates ultrasonic waves modulated by any one of a phase modulation method, an amplitude modulation method, and a frequency modulation method, or a combination thereof, according to the modulated wave output from the modulator 2. can do.

In the following description, the modulator 2 outputs a modulated wave by modulating using two modulation methods, a phase modulation method and an amplitude modulation method, simultaneously, and the piezoelectric element 3 outputs an ultrasonic wave corresponding to the modulated wave. is oscillated.
FIG. 8 shows an example of the waveform of the ultrasonic wave when the piezoelectric element 3 oscillates the ultrasonic wave modulated by simultaneously using the phase modulation method and the amplitude modulation method.

In the following description, the pulse generator 15 oscillates a signal containing an 8-bit code, and the piezoelectric element 3 oscillates a modulated ultrasonic wave containing 8-bit code information. explain.

In FIG. 9, the pulse generator 15 is transmitting a pulse signal containing an 8-bit code [11111000] in order from the most significant bit, and the modulator 2 is arranged bit by bit in order from the upper bit to the lower bit. Waveform of vibration when the piezoelectric element 3 (see FIG. 1) oscillates an ultrasonic wave corresponding to the modulated wave W is exemplified.
Further, FIG. 9 illustrates a case where the modulator 2 modulates the burst length of the corresponding portion with half the burst length of the portion representing 1 in the amplitude modulation method when zero is represented in the amplitude modulation method. is doing.

As can be seen from FIG. 9, in this embodiment, the modulator 2 simultaneously uses at least the phase modulation method and the amplitude modulation method as a plurality of modulation methods to modulate the carrier wave. (long code string) can be transmitted.

Since it is possible to transmit a larger number of transmission bits in a short period of time in this way, it is possible to set a large number of identification signals or identification IDs, and for example, reduce the risk of interference with other distance measuring devices. can be done.

Further, in the present embodiment, transmission of a larger number of transmission bits is possible in a short time, so that the oscillation time T1 can be further shortened if the number of transmission bits is the same (same code string). Therefore, it is possible to shorten the oscillation time T1 and expand the measurement range of the distance measuring device 100 .

[Determination of modulation protocol]
FIG. 1 illustrates a case where another vehicle 200 is oscillating ultrasonic waves for the purpose of obstacle detection, for example. The ultrasonic waves oscillated by vehicle 200 are hereinafter referred to as noise.
If this noise is modulated by the same protocol as the modulation protocol used by the distance measuring device 100, the noise may interfere with the ultrasonic waves oscillated by the distance measuring device 100.

Therefore, in the present embodiment, when the piezoelectric element 3 oscillates the ultrasonic wave to which the identification signal is assigned (the modulator 2 outputs the modulated wave), the distance measuring device 100 uses the piezoelectric element 3 in advance to generate surrounding ultrasonic waves ( For example, the above noise) is received and demodulated by the detector 5, so that the control unit 1 can determine in advance the modulation method of the surrounding ultrasonic waves and the signal contained in the surrounding ultrasonic waves. It is possible to know the ultrasonic wave demodulation signal system, that is, the modulation protocol of the surrounding ultrasonic waves (noise in the case shown in FIG. 1).

Note that when the piezoelectric element 3 oscillates the ultrasonic wave to which the identification signal is assigned, or when the modulator 2 outputs the modulated wave, for example, after the distance measuring device 100 is switched on (power supply is started). After), when the piezoelectric element 3 oscillates first, when the piezoelectric element 3 oscillates intermittently, the piezoelectric element 3 oscillates for a predetermined period or a predetermined number of times, and then the next oscillation is performed. It includes the time when oscillation is started for a predetermined period or a predetermined number of times.

Further, when the ultrasonic wave to which the identification signal is assigned is oscillated from the piezoelectric element 3, "previously" means that the piezoelectric element 3 oscillates, or the reflected wave of the ultrasonic wave to which the identification signal is assigned is oscillated by the piezoelectric element 3 (self). This means that the surrounding ultrasonic waves (noise) are received during a period in which the ultrasonic wave (noise) is not received, and the protocol for modulating the surrounding ultrasonic waves (noise) is known.

Then, the control unit 1 determines the protocol from the demodulated signal and outputs information regarding the protocol of the demodulated signal to the modulator 2 . In this embodiment, as a demodulated signal method, the control unit 1 modulates the modulator 2 with a protocol different from noise, that is, modulates with an ultrasonic modulation method different from noise, or uses an identification signal different from noise ( signal) is given to output the information of the command to modulate.
The modulator 2 modulates the carrier wave with a protocol different from the noise protocol based on the information of the command from the control unit 1 .

A procedure for the control unit 1 (CPU 10) to determine the protocol of the demodulated signal and determine the protocol for modulation will be described below with reference to FIG.
When the distance measurement device 100 starts measurement (step #0), first, it is confirmed whether or not the ultrasonic waves are oscillated for the first time (step #01). Here, the first time refers to the case where the setting of the protocol for ultrasonic waves to be oscillated from now on is not stored in the storage unit 19 . For example, after the switch of the distance measuring device 100 is turned off and the record of the setting of the protocol of the ultrasonic waves to be oscillated in the storage unit 19 is erased (initialized or reset), the distance measuring device 100 is restarted. after the switch is turned on.
If the ultrasonic wave is not oscillated for the first time (step #01: No), the process proceeds to step #11. Step #11 and subsequent steps will be described later.

If the ultrasonic wave is oscillated for the first time (step #01: YES), the process moves to step #02, the surrounding ultrasonic wave is received by the piezoelectric element 3 (step #02), and the comparator 17 detects the wave as the control unit 1. A demodulated signal is acquired from the device 5, the protocol of the surrounding ultrasonic waves is determined (step #03), and the protocol of the ultrasonic waves to be oscillated from now on is set to be different from the protocol of the surrounding ultrasonic waves, and the setting is performed. is recorded in the storage unit 19 .
The controller 1 then transmits the settings to the modulator 2 . The modulator 2 transmits a modulated wave modulated according to the settings to the piezoelectric element 3 . The piezoelectric element 3 that receives the modulated wave oscillates an ultrasonic wave for distance measurement as the distance measurement device 100 .

Step #11 and subsequent steps will be described.
At step #11, the CPU 10, as the control unit 1, reads and acquires the setting of the currently set protocol (hereinafter referred to as the current protocol) from the storage unit 19. FIG.
Next, the control unit 1 receives surrounding ultrasonic waves with the piezoelectric element 3 (step #13).

Next, the comparator 17 as the controller 1 acquires the demodulated signal from the detector 5 and compares it with the current protocol (steps #13 to #15).
At step #13, it is first determined whether the modulation scheme of the demodulated signal matches or does not match the modulation scheme selected in the current protocol.
If they do not match (step #13: No), the process proceeds to step #29 to maintain the current protocol.
If they match (step #13: YES), go to step #14.

At step #14, it is determined whether the bit lengths set in the current protocol match or do not match.
If they do not match (step #14: No), the process moves to step #29 to maintain the current protocol.
If they match (step #14: YES), go to step #15.

At step #15, it is determined whether the bit arrays (codes) set in the current protocol match or do not match.
If they do not match (step #15: No), the process moves to step #29 to maintain the current protocol.
If they match (step #15: YES), go to step #19 and change the protocol.

In this embodiment, when changing the protocol, for example, the modulation method, bit length, and bit arrangement can all be changed.
When the surrounding ultrasonic wave received by the piezoelectric element 3 uses a frequency modulation method, the bit length of the signal included in the surrounding ultrasonic wave is 4 bits, and the bit array is [0101], For example, you can change the protocol as follows.

That is, the amplitude phase modulation method, in which the two modulation methods of the phase modulation method and the amplitude modulation method are simultaneously used for modulation, can be selected as a modulation method different from the frequency modulation method. Furthermore, the bit length of the identification signal can be set to a different bit length from 4 bits, such as 8 bits. Furthermore, the bit array can be set to a bit array different from [0101], such as [11111000]. In this example, the bit array of [0101] of the signal included in the surrounding ultrasonic wave is set so as not to be included in the bit array of [11111000] of the identification signal.

As described above, it is possible to provide a distance measuring device with improved distance measurement performance.

[Another embodiment]
(1) In the above embodiment, the resonance frequency of the piezoelectric element 3 is 40 kHz, but the resonance frequency of the piezoelectric element 3 is not limited to this, and can be arbitrarily set within a sound range (frequency band) exceeding the human audible range. . Note that the sound range exceeding the human audible range refers to, for example, the sound range of ultrasonic waves in a frequency band of 20 kHz or higher.

(2) In the above embodiment, the case where the modulator 2 modulates simultaneously using two modulation methods, ie, the phase modulation method and the amplitude modulation method, has been described.
However, the modulator 2 may simultaneously use the frequency modulation method in addition to the two modulation methods of the phase modulation method and the amplitude modulation method.
Alternatively, the modulator 2 may modulate using any one of the phase modulation method, amplitude modulation method, or frequency modulation method.

(3) In the above embodiment, when the modulator 2 expresses zero in the amplitude modulation method, the burst length of the corresponding portion is modulated with half the burst length of the portion expressing 1 in the amplitude modulation method. explained.
However, even when 0 is represented by the amplitude modulation method, the burst length of the relevant portion may be the same as the burst length of the portion representing 1 by the amplitude modulation method.

(4) In the above embodiment, the case where the predetermined bit length is 8 bits has been exemplified and explained.
However, the bit length can be set arbitrarily, and the bit length required for interference prevention can be selected. For example, the bit length may be 16 bits.

(5) In the above embodiment, the 8-bit signal generated by the pulse generator 15 is sorted by the modulator 2 alternately between the amplitude modulation method and the phase modulation method bit by bit in order from the upper bit to the lower bit. A case of modulation is illustrated.
However, the modulator 2 may modulate and represent the upper 4 bits by phase modulation and the lower 4 bits by amplitude modulation.

(6) In the above embodiment, if the ultrasonic wave is not oscillated for the first time, the process proceeds to step #11 and compares with the current protocol (steps #13 to #15). A case has been described in which the control unit 1 determines match/mismatch in the order of the modulation method, bit length, and bit arrangement of the demodulated signal, and maintains the current protocol when a mismatch is first determined.
However, the control unit 1 can also maintain the current protocol when all of the modulation method, bit length, and bit arrangement of the demodulated signal do not match. In this way, erroneous detection can be prevented more reliably. For example, a signal with a bit array of [0101] and a signal with a bit array of [01010101] have different bit lengths, but even if they contain parts with the same bit array, it is possible to reliably prevent erroneous detection. can be done.

(7) In the above embodiment, one ultrasonic transducer unit is used as the piezoelectric element 3, and when the ultrasonic wave corresponding to the modulated wave is oscillated, the piezoelectric element 3 is used as an oscillating element to generate the surrounding ultrasonic wave. , the same piezoelectric element 3 is used as a vibration receiving element.
However, as shown in FIG. 11, the first probe 31 may be assigned as the receiving element and the second probe 32 (an example of the piezoelectric element unit) as the oscillating element. In this way, while the first probe 31 oscillates ultrasonic waves, the second probe 32 can receive reflected waves and other sound waves. Accuracy can be improved.

In this case, the first probe 31 should be able to receive at least ultrasonic waves, and for example, it can be a unit with a simple configuration optimized for receiving vibrations without requiring a circuit or control necessary for oscillating ultrasonic waves. It should be noted that the unit constituting the first probe 31 can employ a unit other than the piezoelectric element.

Similarly, the second probe 32 only needs to be able to oscillate ultrasonic waves. For example, it can be a unit having a piezoelectric element with a simple configuration without requiring a circuit or control necessary for receiving ultrasonic waves.

(8) In the above embodiment, when changing the protocol different from noise, the case where the modulation method, bit length, and bit arrangement are changed is exemplified.
However, other schemes than or in addition to the modulation scheme, bit length and bit arrangement may be changed. For example, the burst length can be changed to a different burst length than noise.

(9) In the above embodiment, when representing a code, for example, in the case of a phase modulation method, the same phase as the carrier wave represents binary 1, and the phase shifted by π from the carrier wave represents binary zero. A case where the minimum unit is binary is exemplified.
However, the way of representing the codes is not limited to the above example. The code can use other weighted notation besides binary, such as decimal. In addition, each modulation method can also perform modulation exceeding two values.

Specifically, for example, in the case of the phase modulation method, decimal zero (0) is represented in the same phase as the carrier wave, and then decimal 1 is represented in phase shifted by π/4 from the carrier wave. It may also be expressed in four values such that the first phase represents 2 in decimal and the phase shifted by 3π/4 represents 3 in decimal. In this case, instead of decimal numbers, binary numbers may be used as in the above embodiment. For example, binary 00 is represented by the same phase as the carrier wave, then binary 01 is represented by a phase shifted by π/4 from the carrier wave, binary 10 is represented by a phase shifted by π/2, and binary 10 by 3π/4. The out-of-phase can represent 11 in binary.

Similarly, in the case of the amplitude modulation method and the frequency modulation method, it is also possible to employ other weighted notation methods than binary numbers, and to perform modulation beyond binary. For example, in the case of the amplitude modulation method, four levels of amplitude gradation are set, representing four values of binary numbers 00, 01, 10, and 11, or four values of decimal numbers 0, 1, 2, and 3. can also Moreover, it is also possible to set more stages and represent more than four values. Similarly, in the case of the frequency modulation method, it is also possible to set multiple levels of frequency change for the carrier wave to represent multiple values.

(10) In the above embodiment, the pulse generator 15 generates a signal containing a binary code with a predetermined bit length and a predetermined bit array. has been selected, and it has been explained that any array may be selected as the predetermined bit array. In this case, an arbitrary array can include parity bits for error detection.
For example, in the case of a bit length of 8 bits, the most significant bit may be 1 and the least significant bit may be used as a parity bit for error detection. For error detection, for example, an odd parity scheme can be used.
In addition, since the above embodiment enables transmission with a larger number of transmission bits, it is possible to improve identification by using error correction bits instead of using parity bits.

(11) In the above embodiment, when modulated by the amplitude modulation method, if the amplitude is 100% of a relatively large amplitude representing binary 1, 50% of the amplitude is binary A case is exemplified in which modulation control is performed as the target amplitude when representing zero, and binary zero is represented when the amplitude is 75% or less, which is the average value of 100% and 50%.
However, when modulation is performed only by the amplitude modulation method, when representing binary zero, modulation control may be performed with a zero percent amplitude as the target amplitude when representing binary zero. In this case, an amplitude below 50 percent, which is the average of 100 percent and zero percent, for example, may represent a binary zero.

It should be noted that the configurations disclosed in the above embodiments (including other embodiments, the same shall apply hereinafter) can be applied in combination with configurations disclosed in other embodiments as long as there is no contradiction. The embodiments disclosed in this specification are exemplifications, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the object of the present invention.

INDUSTRIAL APPLICABILITY The present invention can be applied to a distance measuring device.

Reference Signs List 1: Control Unit 2: Modulator 3: Piezoelectric Element (Receiving Element, Oscillating Element)
4: Oscillator 5: Detector (demodulator)
9: Object 10: CPU
15: Pulse Generator 17: Comparator 19: Storage Unit 31: First Probe (Receiving Element)
32: Second probe (oscillation element, piezoelectric element unit)
50: FFT circuit 51: ASK demodulator (demodulator)
51a: frequency oscillator 52: FSK demodulator (demodulator)
53: PSK demodulator (demodulator)
53a: frequency oscillator 90: road (object)
91: Obstacle (object)
100: Distance measuring device 200: Vehicle A: Amplitude E: Line Ef: Line P1: Vibration peak P2: Vibration peak T1: Oscillation time T2: Reverberation time Td: Delay time Th: Threshold value W: Waveform

Claims (5)

an oscillator that oscillates a carrier wave;
a modulator that outputs a modulated wave obtained by adding an identification signal to the carrier wave in a predetermined manner;
an oscillation element that oscillates an ultrasonic wave corresponding to the modulated wave;
a receiving element that receives ultrasonic waves;
a demodulator that demodulates the ultrasonic wave received by the receiving element;
A control unit that determines the method of demodulated ultrasonic waves,
The control unit stores a frequency of the carrier wave oscillated by the oscillator and a modulation method of the modulated wave output from the modulator as a protocol setting of the ultrasonic wave to be oscillated by the oscillation element. has a part
When the modulator outputs the modulated wave, the control unit determines whether or not it is the first oscillation based on the setting of the protocol stored in the storage unit,
In the case of the first oscillation, the ultrasonic wave is received by the receiving element in advance, and the received ultrasonic wave is demodulated by the demodulator to obtain a demodulated signal. What is the protocol of the received ultrasonic wave? setting a different protocol and storing it in the storage unit, and outputting information about the setting of the protocol to the modulator;
If it is not the first oscillation, after reading the current protocol settings from the storage unit, the receiving element is made to receive ultrasonic waves in advance, and the received ultrasonic waves are demodulated by the demodulation unit to generate a demodulated signal. and setting a protocol different from the protocol of the received ultrasonic wave based on the comparison result between the protocol of the received ultrasonic wave and the current protocol, and information about the setting of the protocol to the modulator output and
The distance measuring device, wherein the modulator adds the identification signal to the carrier wave in a protocol different from the protocol of the received ultrasonic wave based on the information about the setting of the protocol, and outputs the modulated wave. 2. The distance measuring device according to claim 1, wherein the modulator outputs the modulated wave to which the identification signal having a bit arrangement different from that of the demodulated signal is added. 3. The distance measuring device according to claim 2, wherein the bit array has a bit length different from that of the demodulated signal. The distance measuring device according to any one of claims 1 to 3, wherein the modulator outputs a modulated wave modulated by a method different from the modulation method demodulated by the demodulator. A piezoelectric element unit is provided as the oscillation element,
The distance measuring device according to any one of claims 1 to 4, wherein the vibration receiving element is a unit separate from the piezoelectric element unit.

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